Going head-to-head against his predecessor with the Colts, the 24-year-old quarterback showed everyone he’s more than a worthy replacement for Peyton Manning. He beat Manning at his own game.

On a night that was supposed to belong exclusively to homecoming king, Luck executed a perfect 2-minute drill at the end of the first half, threw three touchdown passes, ran for his third score of the season and kept the Broncos’ defense off balance all night. The result: Indianapolis 39, Denver 33.

“I thought he played really well,” coach Chuck Pagano said of Luck. “I think he had three touchdown passes at half, if I’m not mistaken, 128-something QB rating. There were some errant things in the second half that happened that we’d love to have back. There’s always going to be some plays here and there that you’d love to have back, but I thought he played really well.”

Luck played well enough to hand the Broncos (6-1) their first loss of the season, leaving surprising Kansas City as the NFL’s last unbeaten team. And Luck played well enough to ruin what most expected to be Manning’s chance to prove the Colts (5-2) made a mistake by releasing him in March 2012 so they could rebuild with Luck at the helm.

It was not pure Luck, though he did prove he could thrive under heavy pressure with a prime-time effort.

Here are five other things we learned Sunday night:

FAR FROM PERFECT: Denver may have come into the game with an unbeaten record and Manning seemingly steamrolling to reclaim the touchdown pass record. But Denver is far from the perfect team. The Colts, coming off a Monday night loss in which they didn’t score a touchdown at San Diego, finished with a season-high 39 points and capitalized on just about every mistake the Broncos made. They sacked Manning four times, forced a fumble that turned into a safety and a touchdown and picked him off, too. Afterward, Manning called it a game to learn from.

NEW AND IMPROVED: Colts owner Jim Irsay caught a lot of heat this week for noting that the Colts are building around a different model without Manning. He wanted a more balanced offense, a steadier defense and stronger special teams. It was a big reason the Colts held on Sunday. Indy ran 31 times for 121 yards and kept the ball for more than 31 minutes. Luck still threw for 228 yards and three TDs, and while the defense gave up yards, it limited the NFL’s highest-scoring team to a season-low point total, which forced Denver to play catch-up. Indy had better field position most of the night and it turned a fumbled punt return into a touchdown.

LINE DANCE: Denver has already lost its starting left tackle and its starting center and things have gotten even worse with the loss of right tackle Orlando Franklin (sprained left knee). So, Denver shuffled the lineup and struggled. The question going forward is this: What kind of protection can Manning expect? While that answer will need to be developed over the next several weeks, it’s clear Denver coaches must take another look at what they have. Left tackle Chris Clark was repeatedly burned by speedy pass rusher Robert Mathis, and with the game on the line, Indy’s other outside linebacker, Erik Walden, got his hand on Manning’s arm to force a rare interception.

RISING TO THE OCCASION: With each passing week, the Colts’ defense takes a step forward saving its top performances for its toughest opponents — as Denver found out the hard way. Indy held defending NFC champion San Francisco to seven points, on the road, last month another NFC Super Bowl favorite, Seattle, to just 16 points over the final three quarters after falling into a 12-0 deficit. While they gave up a season-high 33 points to the Broncos, Indy was the first team this season to even slow down Denver’s offense, which spent most of the night trying to play catch-up after averaging more than 44 points per game over the first six weeks.

INJURIES HURT: Neither John Fox nor Chuck Pagano were prepared to say how costly this game might be to their teams. But the two biggest injury concerns are franchise cornerstones. Denver lost cornerback Champ Bailey late in the first half when his left foot got caught in a scrum trying to take down running back Trent Richardson. Bailey angrily walked off the field after re-injuring the same foot that kept him out of the first five games. He did not return. The Colts lost Reggie Wayne in the fourth quarter with a sprained right knee that sent him to the locker room in tears. And while the Colts are hoping for the best, Wayne is expected to undergo an MRI on Monday.